i66 Embryonic Development of Cliironomus 



The outer wall of tlie united folds is called, as in other 

 animals, the serosa ; it forms a complete investment to 



Fig. 1J3. — Diagrams to illustrate the formation of the amnion and serosa of 

 Chironomus-eniljryo. 1, beginning of tail-fold on straight side of egg. 2, tail- 

 fold reaches hinder pole. 3, (after rotation of embryo) head-fold appears on 

 convex side. 4, head-fold growing over anterior pole. 5, coalescence of head- 

 and tail-folds on ventral surface. 6?, blastoderm, y, yolk, f, tail-fold. 7i, head- 

 fold, ap, apex of tail-fold, ap' , apex of head-fold. /, inner embryonic membrane. 

 e, outer ditto. (From Kupfter, Arch. f. luikr. Anat., Bd. ii (1886).) 



the embryo. The inner wall is called amnion or true 

 amnion ; it is continuous, except for a short distance 



